Heat exchanger

ABSTRACT

A heat exchanger has a clad thin sheet material, a clad thick sheet material that is disposed so as to define a passage between the clad thick sheet material and the clad thin sheet material, and that has a sheet thickness greater than that of the clad thin sheet material, and an inner fin held between the clad materials. The clad thick sheet material and the clad thin sheet material have Zn-containing brazing filler metal layers on their passage sides, respectively, and the post-brazing surface Zn amounts are set so as to satisfy specific conditions. Further, certain conditions concerning the compositions of each of the layers that constitute the clad materials, and the inner fin are set.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a heat exchanger that is mounted in an electric automobile or a hybrid automobile, or on any of various electronic device circuits, and that cools a heat-generating device such as a semiconductor device.

2. Description of Related Art

Heat exchangers that cool heat-generating devices such as semiconductor devices are mounted in electric automobiles or hybrid automobiles, or on various electronic device circuits. One example of a conventional heat exchanger of this type is shown in FIG. 4. This heat exchanger 100 is of a water-cooled type, in which cooling water is used as the coolant, and has: a top sheet 102, which is formed of an aluminum alloy sheet, to which to attach a cooling target such as a semiconductor device; a bottom sheet 101 of an aluminum alloy sheet, which defines a passage 104 between the bottom sheet 101 and the top sheet 102; and an inner fin 103, which is held between these aluminum alloy sheets. This heat exchanger 100 cools the cooling target via the top sheet 102 by heat exchange between the inner fin 103 and cooling water flowing within the passage 104. In order to raise the efficiency of heat exchange between the cooling water and the cooling target in this type of heat exchanger 100, the top sheet 102, to which to attach the cooling target, is configured to be sufficiently thinner than the bottom sheet 101. Heat exchangers of this type have also been developed in recent years in which an insulating circuit substrate (the cooling device substrate), on which the semiconductor device (cooling target) is bonded, is attached to the top sheet 102. This insulating circuit substrate has a metal sheet, e.g., pure aluminum, bonded on each side of a thermally conductive insulating ceramic, e.g., AlN or Si₃N₄, and has a function of insulating the semiconductor device from the top sheet 102 while efficiently transferring the heat produced by the semiconductor element to the top sheet 102.

In a heat exchanger 100 with the above-described structure, for example, a clad material having a brazing filler metal layer 101S, 102S on at least the passage 104 side surface is used as the aluminum alloy sheet constituting each of the top sheet 102 and the bottom sheet 101, and the top sheet 102, bottom sheet 101, and inner fin 103 constituting the heat exchanger 100 are brazed together using the brazing filler metal layers 101S, 102S. In the description that follows, the clad material constituting the bottom sheet 101 is also referred to as the “clad thick sheet material” and the clad material constituting the top sheet 102 is also referred to as the “clad thin sheet material”.

The heightened environmental awareness of recent years has resulted in efforts to reduce the weight of automobiles, and a thinning down of the various structural members is thus also underway for the heat exchangers 100 mounted in automobiles. On the other hand, the amount of heat generated by, for example, semiconductor devices, has grown, which has caused an even larger cooling performance to be required of the heat exchangers 100 that cool such semiconductor devices.

This type of heat exchanger 100 has the same corrosive environment as, for example, the radiator ordinarily provided for an engine, and its individual members are exposed to a corrosive environment as a result of contact between the particular member and the cooling water when the cooling water flows. When the constituent members of the heat exchanger 100 are subjected to a severe environment, and particularly in the case of a thinned-down top sheet 102, corrosion develops in the depth direction from the passage 104 side and corrosion pitting may occur more rapidly than the designed service life. This makes it necessary in particular, in order to simultaneously achieve an improved cooling performance and a thinning down of the heat exchanger 100, to improve the corrosion resistance of the top sheet 102, i.e., the clad thin sheet material. A sheet material, in which a core material is clad with a Zn-doped Al—Si brazing filler metal layer or a coating material layer (sacrificial material layer) formed of an Al—Zn alloy has been proposed as a brazing sheet (clad material) with the objective of improving the corrosion resistance of the heat exchanger 100 (refer, for example, to Japanese Patent Application Publication No. 7-41895 (JP 7-41895 A)).

When, in such a case, for example, a clad material having a brazing filler metal layer is used for the top sheet (clad thin sheet material) 102, this is assembled in the heat exchanger 100 with the brazing filler metal layer 102S on the passage 104 side, and brazing is performed, the heat treatment associated with brazing causes the Zn component present in the brazing filler metal layer 102S to diffuse into the core material, thereby forming a concentration gradient of the Zn component in the thickness direction from the surface (surface on the passage 104 side) 102 a of the top sheet 102. The generation of this Zn concentration gradient causes the generation of a potential gradient in the thickness direction from the surface 102 a of the top sheet 102 made of the clad thin sheet material. Cooling water-induced corrosion proceeds preferentially in the surface direction in a top sheet 102 in which such a potential gradient layer has been formed, and the occurrence of corrosion pitting can then be stopped due to an inhibition of corrosion in the depth direction.

However, the following problem can occur when the attempt has been made to use a potential gradient layer to impart corrosion resistance to a top sheet 102 made of a clad thin sheet material in a heat exchanger 100 with the structure described above: even when a heat exchanger 100 has been designed with the goal of forming a corrosion-inhibiting potential gradient layer at the top sheet 102 made of a clad thin sheet material, the intended potential gradient has not always been formed by the clad material after brazing and the anticipated corrosion-inhibiting effect has thus not always been obtained.

SUMMARY OF THE INVENTION

The invention provides a heat exchanger in which a corrosion-inhibiting potential gradient layer can be reliably formed in the individual clad materials that constitute the heat exchanger, thereby yielding an excellent resistance to corrosion caused by the cooling water, and in which corrosion pitting can be inhibited in the neighborhood of a joint region between individual clad materials even when a thin clad sheet material has been used.

A heat exchanger according to a first aspect of the invention has a clad thin sheet material; a clad thick sheet material that is disposed so as to define a passage between the clad thick sheet material and the clad thin sheet material, and that has a sheet thickness greater than that of the clad thin sheet material; and an inner fin held between the clad thick sheet material and the clad thin sheet material, wherein joint regions of these members are joined by brazing; the heat exchanger is configured such that a cooling target to be attached on an opposite side of the clad thin sheet material from the passage is cooled by heat exchange with a cooling water that flows in the passage; the clad thick sheet material has a first core material and a first passage-side brazing filler metal layer that covers a surface of the first core material on a passage side thereof; the clad thin sheet material has a second core material and a second passage-side brazing filler metal layer that covers a surface of the second core material on a passage side thereof; each of the first and second core materials is formed of an aluminum alloy that contains Mn, Cu, and Si in the following contents and contains at least one selected from Fe, Ti, and Zr in the following contents, with the balance being made of Al and unavoidable impurities: Mn: 0.4 to 1.5 mass %, Cu: 0.05 to 0.8 mass %, Si: 0.05 to 1.0 mass %, Fe: 0.05 to 0.5 mass %, Ti: 0.05 to 0.20 mass %, and Zr: 0.05 to 0.15 mass %; each of the first and second passage-side brazing filler metal layers is formed of an aluminum alloy brazing filler metal that contains Si and Zn in the following contents, with the balance being made of Al and unavoidable impurities: Si: 4.5 to 11.0 mass % and Zn: 0.5 to 6.0 mass %; the inner fin is formed of an aluminum alloy that contains Mn and Zn in the following contents and contains at least one selected from Cu, Si, Fe, Ti, and Zr in the following contents, with the balance being made of Al and unavoidable impurities: Mn: 0.8 to 1.5 mass %, Zn: 0.5 to 3.0 mass %, Cu: 0.05 to 0.3 mass %, Si: 0.05 to 1.0 mass %, Fe: 0.05 to 0.5 mass %, Ti: 0.05 to 0.20 mass %, and Zr: 0.05 to 0.20 mass %; and assuming that A₁ is the amount of Zn at the surface of the clad thick sheet material on the passage side thereof after brazing and A2 is the amount of Zn at the surface of the clad thin sheet material on the passage side thereof after brazing, the following conditions are satisfied: A₁: 0.5 to 3.0 mass %, A₂: 0.4 to 2.0 mass %, and A₁>A₂−0.5.

A heat exchanger according to a second aspect of the invention has a clad thin sheet material; a clad thick sheet material that is disposed so as to define a passage between the clad thick sheet material and the clad thin sheet material, and that has a sheet thickness greater than that of the clad thin sheet material; and an inner fin held between the clad thick sheet material and the clad thin sheet material, wherein joint regions of the clad thick sheet material, the clad thin sheet material, and the inner fin are joined by brazing; the heat exchanger is configured such that a cooling target to be attached on an opposite side of the clad thin sheet material from the passage is cooled by heat exchange with a cooling water that flows in the passage; the clad thick sheet material has a first core material and a passage-side brazing filler metal layer that covers a surface of the first core material on the passage side thereof; the first core material is formed of an aluminum alloy that contains Mn, Cu, and Si in the following contents and contains at least one selected from Fe, Ti, and Zr in the following contents, with the balance being made of Al and unavoidable impurities: Mn: 0.4 to 1.5 mass %, Cu: 0.05 to 0.8 mass %, Si: 0.05 to 1.0 mass %, Fe: 0.05 to 0.5 mass %, Ti: 0.05 to 0.20 mass %, and Zr: 0.05 to 0.15 mass %; the passage-side brazing filler metal layer is formed of an aluminum alloy brazing filler metal that contains Si and Zn in the following contents, with the balance being made of Al and unavoidable impurities: Si: 4.5 to 11.0 mass % and Zn: 0.5 to 6.0 mass %; the clad thin sheet material has a second core material and a sacrificial material layer that covers a surface of the second core material on the passage side thereof; the second core material is formed of an aluminum alloy that contains Mn, Cu, and Si in the following contents and that contains at least one selected from Fe, Ti, and Zr in the following contents, with the balance being made of Al and unavoidable impurities: Mn: 0.4 to 1.5 mass %, Cu: 0.05 to 0.8 mass %, Si: 0.05 to 1.0 mass %, Fe: 0.05 to 0.5 mass %, Ti: 0.05 to 0.20 mass %, and Zr: 0.05 to 0.15 mass %; the sacrificial material layer is formed of an aluminum alloy sacrificial material that contains Zn in the following content and contains at least one selected from Si, Fe, Mn, Ti, and Zr in the following contents, with the balance being made of Al and unavoidable impurities: Zn: 0.5 to 5.0 mass %, Si: 0.1 to 1.0 mass %, Fe: 0.05 to 0.5 mass %, Mn: 0.1 to 1.1 mass %, Ti: 0.05 to 0.20 mass %, and Zr: 0.05 to 0.15 mass %; the inner fin is a clad material having a third core material and a fin brazing filler metal layer that covers both sides of the third core material or only the clad thin sheet material side of the third core material, the inner fin being formed of an aluminum alloy that contains Mn and Zn in the following contents and contains at least one selected from Cu, Si, Fe, Ti, and Zr in the following contents, with the balance being made of Al and unavoidable impurities: Mn: 0.8 to 1.5 mass %, Zn: 0.5 to 3.0 mass %, Cu: 0.05 to 0.3 mass %, Si: 0.05 to 1.0 mass %, Fe: 0.05 to 0.5 mass %, Ti: 0.05 to 0.20 mass %, and Zr: 0.05 to 0.20 mass %; the fin brazing filler metal layer is formed of an aluminum alloy brazing filler metal that contains Si and Zn in the following contents, with the balance being made of Al and unavoidable impurities: Si: 5.0 to 12.0 mass % and Zn: 0.5 to 3.0 mass %; and assuming that B1 is the Zn content at the surface of the clad thick sheet material on the passage side thereof after brazing and B2 is the Zn content at the surface of the clad thin sheet material on the passage side thereof after brazing, the following conditions are satisfied: B₁: 0.5 to 3.0 mass %, B₂: 0.4 to 2.0 mass %, and B₁>B₂−0.5.

In the heat exchanger according to the first and second aspects of the invention given above, the clad thin sheet material may have an outer brazing filler metal layer that covers an opposite side of the second core material from the passage, and the outer brazing filler metal layer may be formed of an aluminum alloy brazing filler metal that contains 5.0 to 12.6 mass % of Si, with the balance being made of Al and unavoidable impurities.

The clad thin sheet material may have an outer sacrificial material layer between the second core material and the outer brazing filler metal layer, and the outer sacrificial material layer may be formed of an aluminum alloy sacrificial material that contains Zn in the content given below and contains at least one selected from Si, Fe, Mn, Ti, and Zr in the contents given below, with the balance being made of Al and unavoidable impurities: Zn: 0.5 to 5.0 mass %, Si: 0.1 to 1.0 mass %, Fe: 0.05 to 0.5 mass %, Mn: 0.1 to 1.1 mass %, Ti: 0.05 to 0.20 mass %, Zr: 0.05 to 0.15 mass %.

The results of investigations carried out by the inventors will be described with reference to FIG. 4. According to investigations by the inventors, it has been found that during brazing each of the brazing filler metal layers 101S, 102S on the bottom sheet 101, i.e., the clad thick sheet material, and on the top sheet 102, i.e., the clad thin sheet material, melts and is furnished to the brazing process. However, it has also been found that when this occurs, a portion of the molten brazing filler metal at the bottom sheet 101 present in a position of contact with the top sheet 102 is drawn toward the surface of the top sheet 102 by surface tension and flows via this surface toward the inner fin 103. It is considered that during this sequence the Zn component of the top sheet 102 blends into the molten brazing filler metal L originating from the bottom sheet 101 and is thereby diluted, and as a result the Zn component-induced potential gradient ends up deviating from its design pattern.

Even when, on the other hand, a corrosion-inhibiting potential gradient layer has been formed at the top sheet 102, i.e., the clad thin sheet material, a battery effect is produced in the neighborhood of the joint region where the individual surfaces 101 a, 102 a are in contact when the surface 102 a of the top sheet 102 has a lower potential than the surface 101 a of the bottom sheet 101 in the neighborhood 106 of the joint region between the bottom sheet 101 and the top sheet 102, and corrosion of the top sheet 102 then proceeds preferentially. This results in the problem of corrosion pitting occurring sooner than the number of years of intended durability of the top sheet 102. In addition, investigations have also been carried out into raising the cooling water flow rate in order to raise the cooling efficiency of the heat exchanger 100, but turbulent flow is produced when the cooling water flow rate is made too fast, creating the possibility for erosion or corrosion.

The inventors have acquired the following knowledge as a result of investigations directed to improving the corrosion resistance of the heat exchanger: with regard to the corrosion resistance when brazing sheets with different sheet thicknesses are combined, not only the composition of the individual brazing sheets, but also the influence of the brazing filler metal that flows in from another brazing sheet must be considered; also, the corrosion resistance of each brazing sheet can be clearly and reliably improved, regardless of the brazing conditions, by specifying the amount of surface Zn after brazing for the individual brazing sheets.

Because in the heat exchanger of the invention the clad thick sheet material has a Zn-containing brazing filler metal layer on its passage side and the clad thin sheet material has a Zn-containing brazing filler metal layer on its passage side or a Zn-containing sacrificial material layer on its passage side, the heat treatment for brazing causes the diffusion of the Zn component present in each brazing filler metal layer or present in the sacrificial material layer and thus the formation of a potential gradient layer on the individual passage sides of the clad thick sheet material and the clad thin sheet material. In addition, in the clad thick sheet material and clad thin sheet material, an excellent anticorrosion effect is produced by the potential gradient layer when the post-brazing Zn contents A₁, A₂, B₁, and B₂ of the surfaces (potential gradient layer surface) on the passage sides of the clad thick sheet material and clad thin sheet material satisfy the prescribed conditions. Due to this, corrosion can be reliably inhibited in the heat exchanger of the invention, and as a result corrosion pitting can be effectively inhibited in each clad material and in particular in the clad thin sheet material. Moreover, even when the cooling water flow rate is sped up, erosion and corrosion of each clad material can be reliably inhibited and corrosion pitting of each clad material, and particularly the clad thin sheet material, can be effectively inhibited.

Furthermore, the potential of the passage side surface of the clad thin sheet material is made nobler, or higher, than that of the passage side surface of the clad thick sheet material by setting the Zn content A₂ and B₂ of the passage side surface of the clad thin sheet material so that A₂−0.5 and B₂−0.5 are respectively smaller than the Zn contents A₁ and B₁ of the passage side surface of the clad thick sheet material. This serves to inhibit the battery effect-induced development of corrosion in the clad thin sheet material in the neighborhood of joint regions between individual clad materials and can thereby prevent the occurrence of corrosion pitting in this neighborhood to a joint region. With regard to the clad thick sheet material, its sheet thickness is greater than that of the clad thin sheet material, so that Cu diffusion to the brazing filler metal surface from the core material is relatively small. At the same quantity of Zn, the potential of its surface is then baser, or lower, for the clad thick sheet material than that for the clad thin sheet material. Because of this relation, the relationships of the amounts of Zn at the brazing filler metal surfaces, that is, A₁>A₂−0.5 and B₁>B₂−0.5, are adopted. Accordingly, the heat exchanger of the invention resists corrosion pitting in the clad thin sheet material even when the cooling water flow rate is raised and can simultaneously achieve a thinning down of the individual members and an improved cooling performance.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance of embodiments of the invention will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:

FIG. 1 is a schematic cross-sectional diagram that shows a first embodiment of a heat exchanger of the invention;

FIG. 2 is a schematic cross-sectional diagram that shows a third embodiment of a heat exchanger of the invention;

FIG. 3 is a schematic cross-sectional diagram that shows a fourth embodiment of a heat exchanger of the invention; and

FIG. 4 is a schematic cross-sectional diagram that shows a conventional heat exchanger.

DETAILED DESCRIPTION OF EMBODIMENTS

Specific embodiments of the invention will be described herebelow.

First Embodiment

A first embodiment of the heat exchanger according to the invention will be first described. FIG. 1 is a schematic cross-sectional diagram that shows the first embodiment of a heat exchanger according to the invention. The heat exchanger 10 shown in FIG. 1 is constructed by stacking a clad thick sheet material 1, which forms the bottom sheet, an inner fin 3, and a clad thin sheet material 2, which forms the top sheet, in the given sequence and, using the individual brazing filler metal layers 12, 22 disposed on the interior surfaces of the individual clad materials 1, 2, brazing the clad materials 1, 2 together at the joint regions 13, 23 and brazing the inner fin 3 to the surfaces 1 a, 2 a.

The clad thick sheet material (bottom sheet) 1 and the clad thin sheet material (top sheet) 2 define a passage 4 through which cooling water (coolant) flows. The clad thick sheet material 1 has a sheet shape, and a step portion (joint region) 13, which bonds with the joint region 23 of the clad thin sheet material 2, is intermittently formed at prescribed positions therein. The clad thick sheet material 1 has a sheet thickness that is greater than that of the clad thin sheet material 2, which is described below, and in specific terms is formed in a thickness of about 1.0 to 4.0 mm. The clad thin sheet material 2 is a sheet that assumes a planar shape approximately the same as the clad thick sheet material 1, and a height difference (joint region) 23, which bonds with the joint region 13 of the clad thick sheet material 1, is intermittently formed at prescribed locations therein. The clad thin sheet material 2 has a sheet thickness that is smaller than that of the clad thick sheet material 1, and in specific terms is about 0.2 to 2.0 mm. The clad thick sheet material 1 and the clad thin sheet material 2 are brazed to each other at their respective step portions 13, 23. A coolant passage 4 is defined between the clad thick sheet material 1 and the clad thin sheet material 2 and has a shape bounded by the side walls of the step portions 13, 23. In this embodiment, a composite structure formed of the clad thick sheet material 1 and the clad thin sheet material 2 is adopted because the aforementioned thickness is necessary in order to secure the rigidity as a cooler (heat exchanger) through the use of the clad thick sheet material 1, while a weight reduction and an increase in the cooling performance are obtained through the use of the clad thin sheet material 2.

The inner fin 3 has an accordion-like shape and is held within the passage 4. Each bend (joint region) 33 of the inner fin 3 is brazed to the surface (passage side surface) 1 a, 2 a of the clad thick sheet material 1 or the clad thin sheet material 2. This heat exchanger 10 is configured so that the cooling target is attached to the outside surface (opposite side from the passage 4) 2 b of the clad thin sheet material 2 and can be cooled via the inner fin 3 and the clad thin sheet material 2 by coolant, e.g., cooling water, flowing within the passage 4. In addition, the heat exchanger 10 is configured so that the flow direction of the coolant flowing through the passage 4 is perpendicular to the plane of the sheet on which FIG. 1 is drawn and the inflow and outflow sides of the passage 4 are connected to a coolant circulation device to circulate the coolant via the passage 4.

To produce the heat exchanger 10 described above, for example, a fluoride-based flux (for example, a noncorrosive Nocolok flux or Zn substitution flux) is applied on the clad thick sheet material 1, the clad thin sheet material 2, and the inner fin 3; these are assembled; and a heat treatment is then carried out in an oven having an inert atmosphere, e.g., a nitrogen gas atmosphere. The heat treatment temperature is about 590 to 620° C. By doing this, the brazing filler metal layer on each of the clad materials 1, 2 is melted and flows, and the brazing filler metal is then solidified by reducing the temperature in the oven. As a result, the individual joint regions 13, 23, 33 become brazed and the heat exchanger 10 is thereby obtained.

The substructures and component compositions of the heat exchanger 10 will now be described.

(1) The Clad Thick Sheet Material

The clad thick sheet material 1 has a core material 11 and a brazing filler metal layer 12 that covers the passage 4 side surface of this core material 11. The core material 11 is formed of an aluminum alloy that contains Mn, Cu, and Si and that contains at least one selected from Fe, Ti, and Zr, with the balance being made of Al and unavoidable impurities. The individual component contents are as follows: Mn: 0.4 to 1.5 mass %, Cu: 0.05 to 0.8 mass %, Si: 0.05 to 1.0 mass %, Fe: 0.05 to 0.5 mass %, Ti: 0.05 to 0.20 mass %, and Zr: 0.05 to 0.15 mass %. Their functions are as follows.

Mn: Mn precipitates or crystallizes as an intermetallic compound and has a function of improving the post-brazing strength of the clad thick sheet material 1. In addition, by forming an Al—Mn—Si compound, it has the effect of lowering the Si solid solubility of the aluminum matrix and raising the melting point of the matrix. These effects are not satisfactorily obtained when the Mn content is less than 0.4 mass %. When the Mn content exceeds 1.5 mass %, the casting and processing (rolling) characteristics of the aluminum alloy material decline. Si: Si is present in a solid solution state in the aluminum matrix or dispersed as an Al—Mn—Si compound and has a function of improving the strength of the core material 11. This effect is not satisfactorily obtained when the Si content is less than 0.05 mass %. When the Si content exceeds 1.0 mass %, the melting point of the core material 11 declines and the core material 11 may then melt during brazing.

Cu: Cu is present in a solid solution state in the matrix and has a function of raising the strength of the core material 11. This effect is not satisfactorily obtained when the Cu content is less than 0.05 mass %. When the Cu content exceeds 0.8 mass %, diffusion to the brazing filler metal surface occurs and Cu reduces the sacrificial anode effect of the potential gradient layer, resulting in a loss of its anticorrosion activity. In addition, when the Cu content is too high, the melting point of the core material 11 is reduced and the core material 11 may then melt during brazing. In addition, the strength becomes too high and the press formability is reduced as a result. Fe: Fe precipitates or crystallizes as an intermetallic compound and has a function of increasing the post-brazing strength of the clad thick sheet material 1. In addition, by forming an Al—Mn—Fe, Al—Fe—Si, or Al—Mn—Fe—Si compound, Fe has the effect of lowering the Mn solid solubility and the Si solid solubility in the aluminum matrix and raising the melting point of the aluminum matrix. These effects are not satisfactorily obtained when the Fe content is less than 0.05 mass %. When the Fe content exceeds 0.5 mass %, the corrosion rate of the core material 11 is sped up. In addition, a very large crystalline material appears, which causes a decline in the casting and rolling characteristics of the aluminum alloy material. The unavoidable impurity range for Fe is less than 0.05%.

Ti, Zr: Ti and Zr are dispersed as microscopic intermetallic compounds after brazing and have a function of improving the strength of the clad thick sheet material 1. This effect is not satisfactorily obtained when their content is less than 0.05 mass %. In addition, the processability of the core material 11 declines when the Ti content exceeds 0.20 mass % or when the Zr content exceeds 0.15 mass %. The unavoidable impurity range for Ti and Zr is less than 0.05%.

The brazing filler metal layer 12 supplies brazing filler metal that brazes the joint regions 13, 23 to each other and that brazes the surface 1 a to the bends 33 of the inner fin 3. The brazing filler metal layer 12 is formed of an aluminum alloy brazing filler metal that contains Si and Zn with the balance being made of Al and unavoidable impurities. The Si and Zn contents are Si: 4.5 to 11.0 mass % and Zn: 0.5 to 5.0 mass %, and their functions are as follows.

Si: Si is melted and flows due to the heat treatment in the brazing process, and through its subsequent solidification brazes the joint regions 13, 23 to each other and brazes the surface 1 a to the bends 33 of the inner fin 3. Si has a function of lowering the melting point of the brazing filler metal and a function of raising the fluidity of the brazing filler metal when the brazing filler metal is molten. The brazing capability is inadequate when the Si content is less than 4.5 mass %. When the Si content exceeds 11.0 mass %, eating of the brazing filler metal into the core material 11 or the bonded members 2, 3 becomes severe.

Zn: Zn diffuses into the core material 11 due to the heat treatment accompanying the brazing process and forms a Zn concentration gradient in the thickness direction from the surface 1 a of the clad thick sheet material 1. In addition, since Zn has a relatively lower potential (lower ionization energy), the formation of such a concentration gradient produces a potential gradient in the thickness direction from the surface 1 a of the clad thick sheet material 1. In the case of a clad thick sheet material 1 in which such a potential gradient layer has been formed, when the interior of the passage 4 becomes a corrosive environment due to the cooling water, corrosion proceeds preferentially in the surface direction due to the sacrificial anode effect of the Zn forming the potential gradient and the development of corrosion in the depth direction is inhibited. This makes it possible to obtain an excellent corrosion resistance even under a corrosive environment caused by flow of the cooling water. Moreover, when the brazing filler metal layer 12 of the clad thick sheet material 1 contains Zn, the Zn component of the clad thin sheet material 2 will undergo almost no dilution even when the molten brazing filler metal therefrom flows along the surface 2 a on the inner side of the clad thin sheet material 2. Due to this, a potential gradient layer with an excellent anticorrosion effect can be readily formed at the clad thin sheet material 2 side. A satisfactory potential gradient is not formed when the Zn content is less than 0.5 mass %. When the Zn content exceeds 5.0 mass %, the self-corrosion rate of the potential gradient layer will be too high and the corrosion resistance and erosion resistance of the clad thick sheet material 1 cannot be improved.

In addition, in order to obtain the corrosion resistance as described above, it is important that the clad thick sheet material 1 has an A₁, defined as the post-brazing Zn content of the passage side surface (surface of the potential gradient layer) 1 a, of 0.5 to 3.0 mass % (A₁ is referred to below as the “post-brazing surface Zn amount A₁”). The reason for this will be described in detail below.

(2) The Clad Thin Sheet Material

The clad thin sheet material 2 has a core material 21 and a brazing filler metal layer 22 that covers the passage 4 side surface of this core material 21 and is configured in a manner similar to that in which the clad thick sheet material 1 is configured, except that its thickness is less than one-half that of the clad thick sheet material 1 and A₂, defined as the post-brazing Zn content of the passage side surface 2 a (A₂ is referred to below as the “post-brazing surface Zn amount A₂”), is specified to be 0.4 to 2.0 mass % and to be smaller than the post-brazing surface Zn amount A₁ of the clad thick sheet material 1.

Here, since the clad thin sheet material 2 is thin, corrosion pitting has readily occurred in conventional structures by the development of cooling water-induced corrosion and there has thus been a risk that this will cause holes to open in the heat exchanger 10. In contrast to this, because the clad thin sheet material 2 in the invention has a Zn-containing brazing filler metal layer 22 on the passage 4 side, a potential gradient layer is also formed at the clad thin sheet material 2, just as in the previously described case of the clad thick sheet material 1, by the diffusion of the Zn component of the brazing filler metal layer 22 into the core material 21 due to the heat treatment that accompanies brazing. This serves to inhibit the development of corrosion in the depth direction and as a consequence the occurrence of corrosion pitting, which is a particular problematic in the clad thin sheet material 2, can be inhibited.

In order to obtain this resistance to corrosion pitting, the post-brazing surface Zn amounts A₁, A₂ of the respective clad materials 1, 2 must satisfy the prescribed conditions. The reasons for this will be described in the following. In the invention, as described above, 0.5 to 3.0 mass % is specified for the post-brazing surface Zn amount A₁ of the clad thick sheet material 1 and 0.4 to 2.0 mass % is specified for the post-brazing surface Zn amount A₂ of the clad thin sheet material 2 so that these amounts satisfy the relation, A₁>A₂−0.5. Put differently, the post-brazing surface Zn amounts A₁, A₂ of the clad materials 1, 2 are the surface Zn amounts of the potential gradient layers formed by the heat treatment during brazing. Potential gradient layers that have surface Zn amounts A₁, A₂ in the indicated ranges display an excellent anticorrosion activity and can substantially improve the resistance of the clad materials 1, 2 to corrosion caused by the cooling water.

It is difficult to obtain the intended anticorrosion effect by specifying a Zn content that would provide an anticorrosion effect for each clad material before brazing, because the distribution of the Zn component is altered by diffusion induced by the heating during brazing and by blending with molten brazing filler metal that flows in from another clad material. In contrast to this, when surface Zn amounts A₁, A₂ that will provide an anticorrosion effect are specified for the clad materials 1, 2 after brazing as in the invention, the intended anticorrosion effect can be obtained for the finished heat exchanger 10 because treatments that will change the Zn distribution are not performed after brazing.

In addition, by setting the concentration provided by subtracting 0.5 from the surface Zn amount A₂ of the clad thin sheet material 2 smaller than the surface Zn amount A₁ of the clad thick sheet material 1, the potential of the passage side surface 2 a of the clad thin sheet material 2 is made, due to the influence of the Zn, nobler, or higher, than that of the passage side surface 1 a of the clad thick sheet material 1. This serves to inhibit the battery effect-induced corrosion of the clad thin sheet material 2 in the neighborhood of the joint regions 13, 23 of the clad materials 1, 2 and can thereby prevent the occurrence of the corresponding corrosion pitting. The post-brazing surface Zn amounts A₁, A₂ of the clad thick sheet material 1 and the clad thin sheet material 2 can be adjusted into the prescribed ranges using the component compositions of the individual elements 11, 12, 21, 22, the sheet thickness of the core materials 11, 21, the cladding ratio for the brazing filler metal layers 12, 22, the brazing conditions, and so forth.

(3) The Inner Fin

The inner fin 3 in this embodiment is formed of a bare aluminum alloy that contains Mn and Zn and at least one selected from Cu, Si, Fe, Ti, and Zr, with the balance being made of Al and unavoidable impurities. The contents of the individual components are as follows: Mn: 0.8 to 1.5 mass %, Zn: 0.5 to 3.0 mass %, Cu: 0.05 to 0.3 mass %, Si: 0.05 to 1.0 mass %, Fe: 0.05 to 0.5 mass %, Ti: 0.05 to 0.20 mass %, and Zr: 0.05 to 0.20 mass %. Their functions are as follows.

Mn: Mn precipitates or crystallizes as an intermetallic compound and has a function of improving the post-brazing strength of the inner fin 3. In addition, by forming an Al—Mn—Si compound, it has the effect of lowering the Si solid solubility of the matrix and raising the melting point of the matrix. These effects are not satisfactorily obtained when the Mn content is less than 0.8 mass %. When the Mn content exceeds 1.5 mass %, the casting and processing (rolling) characteristics of the aluminum alloy material decline. Zn: Zn has a function of lowering the potential of the inner fin 3 and to thereby raise the sacrificial anode effect versus the clad materials 1, 2. This effect is not satisfactorily obtained when the Zn content is less than 0.5 mass %. When the Zn content exceeds 3.0 mass %, the self-corrosion rate of the inner fin 3 is too high and the resistance to self-corrosion is reduced.

Cu: Cu is present in a solid solution state in the matrix and has a function of raising the strength of the inner fin 3. This effect is not satisfactorily obtained when the Cu content is less than 0.05 mass %. When the Cu content exceeds 0.3 mass %, Cu, due to its relatively noble potential, or relatively high ionization energy, causes a decline in the sacrificial anode effect of the inner fin 3. In addition, when the Cu content is too high, the melting point of the inner fin 3 is reduced and the inner fin 3 may then melt during brazing. The unavoidable impurity concentration range for Cu is less than 0.05%. Si: Si is present in a solid solution state in the aluminum matrix or dispersed as an Al—Mn—Si compound and has a function of improving the strength of the inner fin 3. This effect is not satisfactorily obtained when the Si content is less than 0.05 mass %. When the Si content exceeds 1.0 mass %, the melting point of the inner fin 3 is reduced and the inner fin 3 may then melt during brazing. In addition, its thermal conductivity is reduced and the heat exchange efficiency of the heat exchanger is then reduced. The unavoidable impurity concentration range for Si is less than 0.05%.

Fe: Fe precipitates or crystallizes as an intermetallic compound and has a function of increasing the post-brazing strength of the inner fin 3. In addition, by forming an Al—Mn—Fe, Al—Fe—Si, or Al—Mn—Fe—Si compound, Fe has the effect of lowering the Mn solid solubility and the Si solid solubility in the matrix and raising the melting point of the matrix. These effects are not satisfactorily obtained when the Fe content is less than 0.05 mass %. When the Fe content exceeds 0.5 mass %, the corrosion rate of the inner fin 3 will end up being too high. In addition, a very large crystalline material appears, which causes a decline in the casting and rolling characteristics of the aluminum material. The unavoidable impurity concentration range for Fe is less than 0.05%.

Ti, Zr: Ti and Zr are dispersed as microscopic intermetallic compounds after brazing and have a function of improving the strength of the inner fin 3. This effect is not satisfactorily obtained when their content is less than 0.05 mass %. In addition, the processability of the inner fin 3 declines when their content exceeds 0.20 mass %. The unavoidable impurity concentration range for Ti and Zr is less than 0.05%.

A potential gradient layer having an excellent anticorrosion effect can be formed on the passage 4 sides of the clad materials 1, 2 in the heat exchanger 10 of this first embodiment as described above because Zn-containing brazing filler metal layers 12, 22 are present on the passage 4 sides of the clad thick sheet material 1 and the clad thin sheet material 2 and because the post-brazing surface Zn amounts A₁, A₂ of the clad materials 1, 2 satisfy the prescribed conditions. As a consequence, even when a structure has been adopted in which cooling water is supplied, corrosion of the clad materials 1, 2 can be reliably inhibited in this heat exchanger 10 and in particular the occurrence of corrosion pitting in the clad thin sheet material 2 can be effectively inhibited.

In addition, by setting the surface Zn amount A₂ of the clad thin sheet material 2 be smaller than the surface Zn amount A₁ of the clad thick sheet material 1, the passage side surface 2 a of the clad thin sheet material 2 takes on a nobler, or higher, potential than that of the passage side surface 1 a of the clad thick sheet material 1 and the development of battery effect-induced corrosion of the clad thin sheet material 2 is inhibited in the neighborhood of the joint regions 13, 23 between the clad materials 1, 2 and the occurrence of the corresponding corrosion pitting can then be prevented. Accordingly, this heat exchanger 10 is resistant to the occurrence of corrosion pitting in the clad thin sheet material 2 even when cooling water flows and can simultaneously achieve a thinning down of the clad thin sheet material 2, an improved cooling performance, and an improved corrosion resistance.

Second Embodiment

A second embodiment of the heat exchanger according to the invention will next be described. Those structures in the second embodiment that are similar to those of the previously described first embodiment will not be described in detail again. The heat exchanger of this second embodiment is configured in a manner similar to that in which the first embodiment is configured, except that, in the heat exchanger 10 in the preceding embodiment, the clad thin sheet material 2 has a sacrificial material layer in place of the brazing filler metal layer 22 and the inner fin 3 is a clad material that has a core material and a brazing filler metal layer that covers only the clad thin sheet material side of the core material or both sides of the core material.

The sacrificial material layer is disposed so as to cover the surface of the passage 4 side of the core material 21. This sacrificial material layer is formed of an aluminum alloy that contains Zn and at least one selected from Si, Fe, Mn, Ti, and Zr, with the balance being made of Al and unavoidable impurities. The contents of the individual components are as follows: Zn: 0.5 to 5.0 mass %, Si: 0.1 to 1.0 mass %, Fe: 0.05 to 0.5 mass %, Mn: 0.1 to 1.1 mass %, Ti: 0.05 to 0.20 mass %, and Zr: 0.05 to 0.15 mass %. The function of each component is as follows.

Zn: Due to the heat treatment accompanying the brazing process, Zn forms a Zn concentration gradient in the thickness direction from the surface 2 a of the clad thin sheet material 2. Because Zn has a relatively lower potential when added to the aluminum matrix, the formation of such a concentration gradient produces a potential gradient in the thickness direction from the surface 2 a of the clad thin sheet material 2. In the case of a clad thin sheet material 2 in which such a potential gradient layer has been formed, due to its sacrificial anode activity, cooling water-induced corrosion proceeds preferentially in the surface direction and the development of corrosion in the depth direction is inhibited. This results in an inhibition of corrosion pitting. A satisfactory potential gradient is not formed when the Zn content is less than 0.5 mass %. Moreover, when the Zn content exceeds 5.0 mass %, the self-corrosion rate of the potential gradient layer will be too high and corrosion of the clad thin sheet material 2 in its depth direction cannot be satisfactorily inhibited. As in the case of the previously described first embodiment, in order to obtain the corrosion resistance as described above, it is important that the post-brazing surface Zn amounts B₁, B2 of the clad materials 1, 2 satisfy prescribed conditions.

Si, Fe, Mn: These components precipitate or crystallize as intermetallic compounds and have a function of improving the post-brazing strength and corrosion resistance of the clad thin sheet material 2. These effects are not satisfactorily obtained when the content of a particular component is less than the lower limit. When the content of a particular component exceeds the upper limit, the corrosion rate of the sacrificial material layer is then too high and the corrosion of the core material cannot be adequately inhibited. Ti, Zr: These components are dispersed as microscopic intermetallic compounds after brazing and have a function of improving the strength of the clad thin sheet material 2. This effect is not satisfactorily obtained when their content is less than 0.05 mass %. In addition, the processability and the resistance to self-corrosion by the sacrificial material layer decline when the Ti content exceeds 0.20 mass % or when the Zr content exceeds 0.15 mass %. In the invention, as described above, 0.5 to 3.0 mass % is specified for the post-brazing surface Zn amount B₁ of the clad thick sheet material 1 and 0.4 to 2.0 mass % is specified for the post-brazing surface Zn amount B₂ of the clad thin sheet material 2 so that these amounts satisfy the relation, B₁>B₂−0.5.

Because, in the heat exchanger of this second embodiment, the clad thick sheet material 1 has a Zn-containing brazing filler metal layer 12 on its passage side and the clad thin sheet material 2 has a Zn-containing sacrificial material layer on its passage side, the Zn component present in the brazing filler metal layer 12 and in the sacrificial material layer diffuses into the core materials 11, 21 due to the heat treatment that accompanies brazing and potential gradient layers are formed on the passage 4 sides of the clad thick sheet material 1 and the clad thin sheet material 2. Moreover, this gradient potential layer exhibits an excellent anticorrosion effect because the post-brazing surface Zn amounts B₁, B₂ of the clad thick sheet material 1 and the clad thin sheet material 2 satisfy the prescribed conditions. As a consequence, even when this heat exchanger has a structure in which cooling water flows, corrosion of each of the clad materials 1, 2 can be reliably inhibited and the occurrence of corrosion pitting in the clad materials 1, 2 and particularly in the clad thin sheet material 2 can be effectively inhibited.

By setting the concentration provided by subtracting 0.5 from the Zn content B₂ of the passage side surface of the clad thin sheet material less than the Zn content B₁ of the passage side surface of the clad thick sheet material, the potential of the passage side surface 2 a of the clad thin sheet material 2 becomes nobler, or higher, than that of the passage side surface 1 a of the clad thick sheet material 1. As a consequence, the development of battery effect-induced corrosion of the clad thin sheet material 2 in the neighborhood of the joint regions between the clad materials 1, 2 is inhibited and the occurrence of corrosion pitting in this neighborhood of the joint regions can be inhibited. Accordingly, in the heat exchanger of the invention, even when the cooling water flow rate is raised, the occurrence of corrosion pitting in the clad thin sheet material is inhibited, so that it is possible to simultaneously achieve a thinning down of the individual members and an increase in the cooling performance.

Third Embodiment

A heat exchanger according to a third embodiment will next be described. No description will be provided for those structures in the third embodiment that are similar to those of the previously described first embodiment. FIG. 2 is a schematic cross-sectional diagram that shows a heat exchanger according to a third embodiment. The heat exchanger 20 in this third embodiment is configured in a manner similar to that in which the previously described first embodiment is configured, except that the clad thin sheet material 2 has a three layer structure that has a brazing filler metal layer 24 on the side opposite from the passage 4.

The brazing filler metal layer 24 is disposed so as to cover the surface 2 b of the core material 21 on the side opposite from the passage 4 side. This brazing filler metal layer 24 is formed of an aluminum alloy brazing filler metal that contains 5.0 to 12.6 mass % of Si with the balance being Al and unavoidable impurities.

Effects similar to those obtained through the previously described first embodiment can also be obtained in this third embodiment. In addition, because in particular the clad thin sheet material 2 in this third embodiment has the brazing filler metal layer 24 on the side opposite from the passage 4, the cooling target can be brazed by this brazing filler metal layer 24 onto the clad thin sheet material 2 in the same step as the brazing step for the various members that constitute the heat exchanger. This has the effect of enabling the cooling unit structure constituted of the heat exchanger 20 and the cooling target to be formed in a short period of time.

While embodiments of the heat exchanger of the invention have been described hereinabove, these are only examples of the various components that make up this heat exchanger, and these components can be modified as appropriate within a range that does not go beyond the scope of the invention. For example, in the heat exchanger of the second embodiment, the clad thin sheet material 2 may have a brazing filler metal layer on the side opposite from the passage 4.

Fourth Embodiment

FIG. 3 shows a heat exchanger 40 according to a fourth embodiment. The clad thin sheet material 2 in the heat exchanger 40 of this embodiment has the same structure as that of the clad thin sheet material 2 in the second embodiment, except

that the clad thin sheet material 2 has a four layer structure that has a brazing filler metal layer 24 and a sacrificial material layer 25 on the opposite side from the passage 4. The brazing filler metal layer 24 in this embodiment is the same as the brazing filler metal layer 24 in the previously described third embodiment, while the sacrificial material layer 25 is the same as the sacrificial material layer in the previously described second embodiment. The structure of this fourth embodiment can provide the effects similar to those obtained through the heat exchanger of the second embodiment.

There are no particular limitations on the cooling target attached on the clad thin sheet material on the side opposite from the passage in the heat exchanger of the invention. Examples of the cooling target include heat-generating devices such as semiconductor devices, composite structures provided by bonding a heat-generating device to the surface of a cooling device substrate (for example, an insulating circuit substrate provided by bonding an aluminum layer on each side of a thermally conductive ceramic, e.g., AlN or Si₃N₄). These cooling targets may be brazed to the heat exchanger after its production or may be brazed in the same step as the brazing step for the various members constituting the heat exchanger.

Specific examples of the invention are described below. However, the invention is not limited to these examples. A bottom sheet was used that had the cross-sectional shape shown in FIG. 1; it was prepared by cladding a 3 mm-thick aluminum alloy core material having the alloy components shown in Table 1 with a 160 μm-thick brazing filler metal layer having the composition shown in Table 1 by pressure-bonding. A top sheet was used that had the cross-sectional shape shown in FIG. 1; it was prepared by cladding both the front and back sides of a 0.6 mm-thick aluminum alloy core material having the alloy components shown in Table 2 with a 70 gm-thick brazing filler metal layer having the composition shown in Table 2 by pressure-bonding. A 0.5 mm-thick fin with the corrugated shape shown in FIG. 1 was used; its composition is shown in Table 4. This bottom sheet, top sheet, and fin were assembled into the heat exchanger configuration shown in FIG. 1 and a heat exchanger was obtained by brazing by heating for 1 to 15 minutes at 580 to 615° C. as shown in Table 5. A heat exchanger was also obtained by assembling a bottom sheet with the alloy composition shown in Table 1, a top sheet provided with a sacrificial material layer (thickness=70 μm) and a brazing filler metal layer (thickness=70 μm) with the alloy composition in Table 3, and an inner fin (brazing filler metal layer thickness=40 μm) with the alloy composition shown in Table 4 into a heat exchanger configuration and carrying out brazing under the conditions shown in Table 5. The following are reported below in Tables 5 and 6 for these heat exchanger samples: the brazing conditions, the surface Zn amount (A₁) of the clad thick sheet material, the surface Zn amount (A₂) of the clad thin sheet material, the size relationship between A₁ and A₂, and the results of corrosion testing. The corrosion testing conditions are as follows. Corrosion solution: ion-exchanged water+(Cl⁻: 100 ppm, SO₄ ²⁻: 300 ppm, Cu⁺⁺: 50 ppm) adjusted with NaCl, Na₂SO₄, and CuCl₂. Corrosion test: repetition of a (circulation) process in which 60 liters of the corrosion solution is circulated (80° C. for 8 hours) in the core and a circulation stop process at room temperature for 16 hours; different flow rates (L/min) are used. Evaluation: measurement of the depth of the largest corrosion pit feature.

TABLE 1 core material brazing filler metal clad thick Mn Cu Si Fe Ti Zr Si Zn sheet material 0.4 to 1.5 0.05 to 0.8 0.05 to 1.0 0.05 to 0.5 0.05 to 0.20 0.05 to 0.15 4.5 to 11.0 0.5 to 6.0 Example 1 0.42 0.79 0.05 0.05 0.05 4.5 5.5 2 0.6 0.7 0.1 0.12 0.12 0.1 5.5 4.5 3 1.0 0.3 0.16 0.5 5.9 2.8 4 1.3 0.5 0.2 0.4 5.1 5.1 5 1.5 0.13 0.3 0.35 6.8 4.5 6 1.1 0.13 0.3 0.41 7.5 0.6 7 1.2 0.12 0.3 0.18 7.5 3.2 8 1.3 0.09 0.4 0.16 9.5 1.2 9 1.2 0.07 0.8 0.15 10 5.1 10  1.2 0.1 0.95 0.12 11 5.6 Comparative 0.35 0.04* 0.02* 0.03 0.08 3.2* 3.4 Example 1 2 1.1 0.9* 0.25 0.1 4.3 0.3* 3 1.2 0.15 0.23 11.5* 0.3* 4 1.2 0.2 0.25 7.5 6.4* 5 1.3 0.21 0.28 0.18* 7.5 0.6 6 1.65* 0.4 1.1* 0.56* 0.25* 11.5* 3.4 (composition: mass %)

TABLE 2 brazing filler metal brazing filler metal on the core material on the passage side opposite side from the passage clad thin Mn Cu Si Fe Ti Zr Si Zn present/ Si sheet material 0.4 to 1.5 0.05 to 0.8 0.05 to 1.0 0.05 to 0.5 0.05 to 0.20 0.05 to 0.15 4.5 to 11.0 0.5 to 6.0 absent 5.0 to 12.6 Example 1 0.42 0.78 0.06 0.43 0.1 0.1 4.8 0.7 absent 2 0.92 0.6 0.13 0.21 5.6 0.8 absent 3 1.1 0.5 0.24 9.6 1.3 absent 4 1.2 0.5 0.25 0.19 7.5 2.5 present 5.3 5 1.3 0.12 0.4 0.07 7.5 5.4 present 10.6 6 1.2 0.34 0.45 0.1 8.9 4.3 present 10.3 7 1.3 0.08 0.67 0.13 10.9 3.7 present 7.5 8 1.5 0.06 0.99 0.12 7.5 3.5 present 8.9 Comparative 0.35* 0.2 0.02 0.32 7.5 0.3* absent 5.6 Example 1 2 1.6* 0.23 0.25 0.04 7.5 6.9* absent 6.7 3 1.3 0.02* 0.39 4.1* 3.2 present 9.4 4 1.2 0.89* 1.2 0.56 0.26 0.15 12.1* 3.2 present 10.3 5 1.1 0.17 0.23 0.32 4.3* 0.5* present 10.1 (composition: mass %)

TABLE 3 sacrificial material on brazing filler metal on the core material passage side opposite side from the passage Mn Cu Si Fe Ti Zr Zn Si Fe Mn Ti Zr Si clad thin 0.4 0.05 0.05 0.05 0.05 0.05 0.5 0.1 0.05 0.1 0.05 0.05 present/ 5.0 sheet material to 1.5 to 0.8 to 1.0 to 0.5 to 0.20 to 0.15 to 5.0 to 1.0 to 0.5 to 1.1 to 0.20 to 0.15 absent to 12.6 Example 9 0.42 0.78 0.06 0.43 0.1 0.1 0.8 1 0.07 1 0.05 absent 10 0.92 0.6 0.13 0.21 1.8 0.5 0.19 0.7 0.05 absent 11 1.1 0.5 0.24 3.5 0.7 0.34 0.5 0.15 absent 12 1.2 0.5 0.25 0.19 4.7 0.3 0.3 0.12 0.1 0.14 present 5.3 Comparative 1.3 0.12 0.04 0.07 0.2 0.3 0.2 0.3 absent Example 6  7 1.3 0.12 0.04 0.07 5.5 0.3 0.2 0.1 0.1 absent (composition: mass %)

TABLE 4 brazing filler metal core material both sides/ Mn Zn Cu Si Fe Ti Zr one side/ Si Zn inner fin 0.8 to 1.5 0.5 to 3.0 0.05 to 0.3 0.05 to 1.0 0.05 to 0.5 0.05 to 0.20 0.05 to 0.20 absent 5.0 to 12.0 0.5 to 3.0 Example 1 1.2 0.6 0.05 both sides 6.7 1.5 2 0.9 2.5 0.96 0.34 0.12 one side 11.5 2.7 3 1.4 2.8 0.29 0.34 0.19 0.1 absent Comparative 1.2 0.2* 0.1 0.1 0.23 0.1 absent Example 1 2 1.2 3.9* 0.1 0.43 both sides 6.7 1.5 3 1.2 1.5 0.5* 0.05 0.1 one side 11.5 2.7 (composition: mass %)

TABLE 5 surface Zn amount clad thick clad thin for the clad thick sheet sheet brazing sheet material material inner fin material conditions A₁ 0.5 to 3.0% Example A Example 1 Example 3 Example 1 580° C. × 3 7 min B Example 2 Example 3 Example 2 600° C. × 2.9 10 min C Example 3 Example 3 Example 3 610° C. × 2.8 10 min D Example 4 Example 3 Example 4 615° C. × 1.6 15 min E Example 5 Example 3 Example 5 620° C. × 3 1 min F Example 6 Example 3 Example 6 600° C. × 2.2 3 min G Example 7 Example 3 Example 7 600° C. × 1.8 3 min H Example 8 Example 3 Example 8 600° C. × 2.4 3 min I Example 9 Example 1 Example 9 600° C. × 2.9 (sacrificial) 3 min J Example 10 Example 1 Example 10 600° C. × 2.4 (sacrificial) 3 min K Example 7 Example 2 Example 11 600° C. × 1.8 (sacrificial) 3 min L Example 7 Example 2 Example 12 600° C. × 1.7 (sacrificial) 3 min Comparative Comparative Example 1 Example 5 600° C. × 3.1 Example a Example 1 3 min b Comparative Example 1 Example 5 600° C. × 2.8 Example 2 3 min c Comparative Comparative Example 7 600° C. × 1.8 Example 3 Example 1 3 min d Comparative Example 1 Example 8 600° C. × 1.8 Example 4 3 min e Comparative Example 1 Example 5 600° C. × Example 5 3 min f Comparative Example 1 Example 5 600° C. × Example 6 3 min g Example 7 Example 1 Comparative 600° C. × 1.8 Example 1 3 min h Example 7 Example 1 Comparative 600° C. × 3 Example 2 3 min i Example 7 Example 1 Comparative 600° C. × 1.6 Example 3 3 min j Example 7 Comparative Comparative 600° C. × 1.6 Example 1 Example 4 3 min k Example 7 Comparative Comparative 600° C. × 1.5 Example 1 Example 5 3 min l Example 7 Comparative Comparative 600° C. × 2.1 Example 2 Example 6 3 min m Example 7 Comparative Comparative 600° C. × 2 Example 3 Example 7 3 min

TABLE 6 surface Zn amount of A₁, the clad thin A₂ − 0.5 sheet material A₁ > corrosion test A₂ 0.4 to 2.0 A₂ − 0.5 flow rate depth evaluation remarks Example A 2 A₁ > 10 L/min 120 μm OK A₂ − 0.5 B 1.8 A₁ > 10 L/min 130 μm OK A₂ − 0.5 C 1 A₁ > 10 L/min 100 μm OK A₂ − 0.5 D 1.2 A₁ > 10 L/min  90 μm OK A₂ − 0.5 E 2.0 A₁ > 15 L/min  80 μm OK A₂ − 0.5 F 0.4 A₁ > 20 L/min 165 μm OK A₂ − 0.5 G 1.6 A₁ > 30 L/min 139 μm OK A₂ − 0.5 H 1.2 A₁ > 10 L/min 101 μm OK A₂ − 0.5 I 0.4 B₁ > 10 L/min 106 μm OK B₂ − 0.5 J 0.6 B₁ > 10 L/min 183 μm OK B₂ − 0.5 K 2.2 B₁ > 10 L/min 156 μm OK B₂ − 0.5 L 2.1 B₁ > 10 L/min 177 μm OK B₂ − 0.5 Comparative 2.4 A₁ > 10 L/min leakage NG brazing capacity Example a A₂ − 0.5 NG defective joint region brazing due to Si deficiency in the thick sheet brazing filler metal

 Leakage is produced at joint regions due to deficient fillet formation.) b 0.2 A₁ > — press molding NG A₂ − 0.5 (strength increased due to excess Cu), corrosion resistance NG (sacrificial anticorrosion effect reduced due to excess Cu), corrosion resistance impaired by brazing filler metal Zn deficiency c 0.1 A₁ > 10 L/min leakage NG top sheet leakage A₂ − 0.5 (corrosion resistance impaired due to brazing filler metal Zn deficiency) d 3.2 A₁ < 10 L/min leakage NG leakage produced A₂ − 0.5 at top sheet and joint regions (top sheet corrosion, joint region preferential corrosion due to reversed Zn amount) e — rollability NG (impaired processability due to excess Zr) f — rollability NG (impaired rollability due to excess Mn) g 0.1 A₁ > 10 L/min leakage NG leakage at the top A₂ − 0.5 sheet (deficient potential difference due to brazing filler metal Zn deficiency) h 3.5 A₁ = 10 L/min leakage NG reduced rollability A₂ − 0.5 (impaired rollability due to excess Mn), leakage at joint regions(preferential corrosion at joint regions due to brazing filler metal Zn excess) i 2.0 A₁ < defective top sheet A₂ − 0.5 brazing (Si deficiency in the top sheet brazing filler metal) j 0.3 A₁ > 10 L/min leakage NG leakage at the top A₂ − 0.5 sheet (due to Si excess in the top sheet brazing filler metal, decline in surface Zn amount in brazing filler metal 

 corrosion leakage, inner fin Zn deficiency) k 0.3 A₁ > 10 L/min leakage NG leakage at the top A₂ − 0.5 sheet (decline in surface Zn amount in brazing filler metal due to Zn deficiency in the brazing filler metal

 corrosion leakage) l 0.1 B₁ > 10 L/min leakage NG leakage at the top B₂ − 0.5 sheet(reduced corrosion resistance due to Zn deficiency in the sacrificial material 

corrosion leakage) m 3.2 B₁ < 10 L/min leakage NG leakage at top sheet B₂ − 0.5 (rapid disappearance of sacrificial material due to Zn excess in the sacrificial material 

corrosion leakage)

Examples A to L, which were within the ranges specified by the invention, in all instances were able to withstand the corrosion test and did not produce leakage. In contrast to this, leakage was produced by the heat exchanger samples of Comparative Examples d, h, i, and m, in which the Zn amounts satisfy the relationship, A₁≦A₂−0.5 (B₁≦B₂−0.5). 

1. A heat exchanger, characterized by comprising: a clad thin sheet material; a clad thick sheet material that is disposed so as to define a passage between the clad thick sheet material and the clad thin sheet material, and that has a sheet thickness greater than that of the clad thin sheet material; and an inner fin held between the clad thick sheet material and the clad thin sheet material, wherein: joint regions of the clad thick sheet material, the clad thin sheet material, and the inner fin are joined by brazing; the heat exchanger is configured such that a cooling target to be attached on an opposite side of the clad thin sheet material from the passage is cooled by heat exchange with a cooling water that flows in the passage; the clad thick sheet material has a first core material and a first passage-side brazing filler metal layer that covers a surface of the first core material on a passage side thereof; the clad thin sheet material has a second core material and a second passage-side brazing filler metal layer that covers a surface of the second core material on a passage side thereof; each of the first and second core materials is formed of an aluminum alloy that contains Mn, Cu, and Si in contents given below and contains at least one selected from Fe, Ti, and Zr in contents given below, with the balance being made of Al and unavoidable impurities Mn: 0.4 to 1.5 mass % Cu: 0.05 to 0.8 mass % Si: 0.05 to 1.0 mass % Fe: 0.05 to 0.5 mass % Ti: 0.05 to 0.20 mass % Zr: 0.05 to 0.15 mass %; each of the first and second passage-side brazing filler metal layers is formed of an aluminum alloy brazing filler metal that contains Si and Zn in contents given below, with the balance being made of Al and unavoidable impurities Si: 4.5 to 11.0 mass % Zn: 0.5 to 6.0 mass %; the inner fin is formed of an aluminum alloy that contains Mn and Zn in contents given below and contains at least one selected from Cu, Si, Fe, Ti, and Zr in contents given below, with the balance being made of Al and unavoidable impurities Mn: 0.8 to 1.5 mass % Zn: 0.5 to 3.0 mass % Cu: 0.05 to 0.3 mass % Si: 0.05 to 1.0 mass % Fe: 0.05 to 0.5 mass % Ti: 0.05 to 0.20 mass % Zr: 0.05 to 0.20 mass %; and assuming that A1 is an amount of Zn at the surface of the clad thick sheet material on the passage side thereof after brazing and A2 is an amount of Zn at the surface of the clad thin sheet material on the passage side thereof after brazing, following conditions are satisfied: A1: 0.5 to 3.0 mass % A2: 0.4 to 2.0 mass % A₁>A₂−0.5.
 2. A heat exchanger, characterized by comprising: a clad thin sheet material; a clad thick sheet material that is disposed so as to define a passage between the clad thick sheet material and the clad thin sheet material, and that has a sheet thickness greater than that of the clad thin sheet material; and an inner fin held between the clad thick sheet material and the clad thin sheet material, wherein: joint regions of the clad thick sheet material, the clad thin sheet material, and the inner fin are joined by brazing; the heat exchanger is configured such that a cooling target to be attached on an opposite side of the clad thin sheet material from the passage is cooled by heat exchange with a cooling water that flows in the passage; the clad thick sheet material has a first core material and a passage-side brazing filler metal layer that covers a surface of the first core material on a passage side thereof; the first core material is formed of an aluminum alloy that contains Mn, Cu, and Si in contents given below and contains at least one selected from Fe, Ti, and Zr in contents given below, with the balance being made of Al and unavoidable impurities Mn: 0.4 to 1.5 mass % Cu: 0.05 to 0.8 mass % Si: 0.05 to 1.0 mass % Fe: 0.05 to 0.5 mass % Ti: 0.05 to 0.20 mass % Zr: 0.05 to 0.15 mass %; the passage-side brazing filler metal layer is formed of an aluminum alloy brazing filler metal that contains Si and Zn in contents given below, with the balance being made of Al and unavoidable impurities Si: 4.5 to 11.0 mass % Zn: 0.5 to 6.0 mass %; the clad thin sheet material has a second core material and a sacrificial material layer that covers a surface of the second core material on a passage side thereof; the second core material is formed of an aluminum alloy that contains Mn, Cu, and Si in contents given below and contains at least one selected from Fe, Ti, and Zr in contents given below, with the balance being made of Al and unavoidable impurities Mn: 0.4 to 1.5 mass % Cu: 0.05 to 0.8 mass % Si: 0.05 to 1.0 mass % Fe: 0.05 to 0.5 mass % Ti: 0.05 to 0.20 mass % Zr: 0.05 to 0.15 mass %; the sacrificial material layer is formed of an aluminum alloy sacrificial material that contains Zn in a content given below and contains at least one selected from Si, Fe, Mn, Ti, and Zr in contents given below, with the balance being made of Al and unavoidable impurities Zn: 0.5 to 5.0 mass % Si: 0.1 to 1.0 mass % Fe: 0.05 to 0.5 mass % Mn: 0.1 to 1.1 mass % Ti: 0.05 to 0.20 mass % Zr: 0.05 to 0.15 mass %; the inner fin is a clad material having a third core material and a fin brazing filler metal layer that covers both sides of the third core material or only the clad thin sheet material side of the third core material, the inner fin being formed of an aluminum alloy that contains Mn and Zn in contents given below and contains at least one selected from Cu, Si, Fe, Ti, and Zr in contents given below, with the balance being made of Al and unavoidable impurities Mn: 0.8 to 1.5 mass % Zn: 0.5 to 3.0 mass % Cu: 0.05 to 0.3 mass % Si: 0.05 to 1.0 mass % Fe: 0.05 to 0.5 mass % Ti: 0.05 to 0.20 mass % Zr: 0.05 to 0.20 mass %; the fin brazing filler metal layer is formed of an aluminum alloy brazing filler metal that contains Si and Zn in contents given below, with the balance being made of Al and unavoidable impurities Si: 5.0 to 12.0 mass % Zn: 0.5 to 3.0 mass %; and assuming that B1 is a Zn content at the surface of the clad thick sheet material on the passage side thereof after brazing and B2 is a Zn content at the surface of the clad thin sheet material on the passage side thereof after brazing, following conditions are satisfied B1: 0.5 to 3.0 mass % B2: 0.4 to 2.0 mass % B₁>B₂−0.5.
 3. The heat exchanger according to claim 1, wherein the clad thin sheet material has an outer brazing filler metal layer that covers an opposite side of the second core material from the passage, and the outer brazing filler metal layer is formed of an aluminum alloy brazing filler metal that contains 5.0 to 12.6 mass % of Si, with the balance being made of Al and unavoidable impurities.
 4. The heat exchanger according to claim 3, wherein the clad thin sheet material has an outer sacrificial material layer between the second core material and the outer brazing filler metal layer, and the outer sacrificial material layer is formed of an aluminum alloy sacrificial material that contains Zn in a content given below and contains at least one selected from Si, Fe, Mn, Ti, and Zr in contents given below, with the balance being made of Al and unavoidable impurities Zn: 0.5 to 5.0 mass % Si: 0.1 to 1.0 mass % Fe: 0.05 to 0.5 mass % Mn: 0.1 to 1.1 mass % Ti: 0.05 to 0.20 mass % Zr: 0.05 to 0.15 mass %.
 5. The heat exchanger according to claim 2, wherein the clad thin sheet material has an outer brazing filler metal layer that covers an opposite side of the second core material from the passage, and the outer brazing filler metal layer is formed of an aluminum alloy brazing filler metal that contains 5.0 to 12.6 mass % of Si, with the balance being made of Al and unavoidable impurities.
 6. The heat exchanger according to claim 5, wherein the clad thin sheet material has an outer sacrificial material layer between the second core material and the outer brazing filler metal layer, and the outer sacrificial material layer is formed of an aluminum alloy sacrificial material that contains Zn in a content given below and contains at least one selected from Si, Fe, Mn, Ti, and Zr in contents given below, with the balance being made of Al and unavoidable impurities Zn: 0.5 to 5.0 mass % Si: 0.1 to 1.0 mass % Fe: 0.05 to 0.5 mass % Mn: 0.1 to 1.1 mass % Ti: 0.05 to 0.20 mass % Zr: 0.05 to 0.15 mass %. 